On Thu, 2007-09-13 at 21:54 +0100, Bijan Parsia wrote:
> Yes. It's not a mapping from DL to LP. But from DL to Horn Logic.
(restricted) DL -> definite Horn -> definite Logic Programming (ground,
fact-forming entailments only)
> > It is defined as a function whose input are DL expressions
> > (an expressive subset: DHL) and the output is "equivalent" Horn Logic.
> >
> >> LP to FOL, look at
> >> things like clark's completion.
> >
> > DHL is in the other direction, no?
>
> DHL? DLP? For them to be meaning preserving they need to be
> bilateral, eh?
> But I don't know of a way (at least a standard way) to go from first
> order horn (without function symbols) to Datalog under LP semantics
> for beyond ground entailments. My intuition sez it'd be pretty bad.
I would agree about this being problematic. But (thinking out loud) at
least where the evaluation is being performed by a production rule
system, couldn't you simply skolemize the existential variables in the
conclusion set?
/me wonders what the appropriate forum is for these kinds of questions
> > is a very important contribution towards reducing the
> > (currently) intractable nature of inference over large ontologies
> > (especially EL++ ontologies
>
> It's not intractable currently. See CEL and Hermit.
Okay then, how about http://www.cyc.com/2004/06/04/cyc ? :)
> DLP is not really very helpful for dealing with EL++. EL++ is already
> well known to be horn and there are several techniques for dealing
> with it. The latest is hypertableau. See the link from my blog post:
> <http://clarkparsia.com/weblog/2007/06/25/scaling-owl-two-new-ways/>
My interest in DLP (and others as well), is not simply that it gives you
an alternative way to evaluate certain fragments of DL, but that it does
this by *mapping* to a rule language in such a way that if your primary
mechanism for evaluation is (for instance) a production rule system you
can use rules (which capture semantics outside of what DL is capable of)
in combination with ontologies. This is incredibly useful for decision
support (contrary to your claim below). Bear in mind, DL is a KR with
explicitly-engineered restrictions in expressiveness, so by definition
there will be semantics (useful to certain domains) that it cannot
express.
> I know you're really into it, but DLP is quite the uninteresting Horn
> Description Logic, esp. for Life Sciences.
That's a bit harsh (and perhaps unsubstantiated). On what concrete
basis is it uninteresting, Bijan? In the ACPP task group we found
*many* guideline and workflow semantics that are trivial to express in
rule languages and (in many cases) impossible to express in any variety
of DL. When you consider the combination of 'open-ended' rules with
rules you can extract (while preserving meaning) from expressive
fragments of Description Logic (which includes EL++), this results in a
*very* versatile KR, IMHO.
> (I think the worst thing about the DLP paper is that damn shield
> diagram which is one of the top 15 misleading diagrams out there.
> It's very seductive but really overall hurts ones understanding of
> the relationship between the various logics.)
I happen to like that diagram, care to elaborate :)
--
Chimezie Ogbuji
Lead Systems Analyst
Thoracic and Cardiovascular Surgery
Cleveland Clinic Foundation
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